1. Field of the Invention
This invention relates to a liquid crystal display, and more particularly to a liquid crystal display device that is capable of preventing metal wires from being corroded during its long-term use under the high temperature and high humidity circumstance. The present invention also is directed to a method of fabricating such a liquid crystal display device.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) of active matrix driving system uses thin film transistors (TFT""s) as switching devices to display a natural moving picture. Since such a LCD can be made into a smaller device in size than the existent Brown tube, it has been widely used for a monitor for a personal computer or a notebook computer as well as an office automation equipment such as a copy machine, etc. and a portable equipment such as a cellular phone and a pager, etc.
A method of fabricating such an active matrix LCD is classified into substrate cleaning, substrate patterning, aligning film formation, substrate adhesion/liquid crystal injection, packaging and test processes.
In the substrate cleaning process, a cleaner removes an alien substance on the substrates before and after patterning of the upper and lower substrate.
The substrate patterning process is divided into a step of patterning the upper substrate and a step of patterning the lower substrate. The upper substrate is provided with color filters, a common electrode and a black matrix, etc. The lower substrate is provided with signal wires such as data lines and gate lines, etc. A thin film transistor (TFT) is arranged at each intersection between the data lines and the gate lines. A pixel electrode is formed at each pixel area between the data lines and the gate lines to be connected to a source electrode of the TFT.
In the substrate adhesion/liquid crystal injection process, a step of coating an aligning film on the lower substrate and rubbing it is sequentially followed by a step of adhering the upper substrate to the lower substrate, a liquid crystal injection step and an injection hole sealing step.
In the packaging process, a tape carrier package (TCP) mounted with a gate drive integrated circuit (IC) and a data drive IC, etc. is connected to a pad portion on the substrate.
Finally, in the test process, an operation state of a driver IC chip mounted or patterned on the substrate to drive the gate lines and the data lines is tested so as to detect a bad pixel.
In the LCD device, a metal thin film pattern may be corroded during its fabrication process or during its use. Particularly, a corrosion is liable to be generated at a patterned driver circuit, a pad for testing a driver IC mounted onto the TCP, a shorting bar pattern connected to a gate pad and a data pad or an electrode pad exposed by a grinding of the substrate.
The TFT is divided into an amorphous silicon type and a poly silicon type depending on a kind of material used as its semiconductor layer. The amorphous silicon type TFT has advantages of a relatively good uniformity and a stable characteristic while having a drawback of low electric charge mobility. Also, a use of the amorphous silicon type TFT causes a problem in that the peripheral driving circuits are mounted onto the display panel after being manufactured separately. On the other hand, the poly silicon type TFT has advantages in that, since it has a high electric charge mobility, it is not only easy to increase a pixel density, but also the peripheral driving circuits are directly mounted onto the display panel.
Referring to FIG. 1, a conventional poly silicon type LCD device includes an upper substrate 2 and a lower substrate 1 joined with each other with having a liquid crystal therebetween, a gate driver IC 9 patterned on the lower substrate 1 to drive a gate line (not shown), and a pad 6 connected, via a link pattern 4, to the gate driver IC 9. The edges of the upper substrate 2 and the lower substrate 1 joined with each other are coated with a seal 7. A liquid crystal is injected into a display area between the upper substrate 2 and the lower substrate 1. A poly silicon layer is formed on the lower substrate 1, and the TFT, the data line, the gate line and the pixel electrode, etc. are disposed thereon.
The gate driver IC 9 is directly patterned on the upper substrate 1 positioned at the inside of the seal 7. The gate driver IC 9 is connected to the gate lines and/or the data lines. The gate driver IC 9 applies a test voltage coupled via the pad 6 and the link pattern 4 to the gate line during the test process.
The pad 6 includes a metal thin film pattern 3, and a transparent conductive pattern 5 patterned along with a pixel electrode (not shown). The metal thin film pattern 3 is formed on a gate insulating film la made from an inorganic insulating material and is patterned along with source/drain electrodes of the TFT, the data line connected to the source electrode and the link pattern 4 as shown in FIG. 2. The transparent conductive pattern 5 is connected, via a contact hole 10 defined in a passivation layer made from an inorganic insulating material or an organic insulating material, to the metal thin film pattern 3.
A crack or a film stripping may be generated between the metal thin film pattern 3 and the transparent conductive pattern 5 of the pad 6 due to an impact, etc. during the fabrication process of the LCD device. When a crack or a film stripping has been generated between the metal thin film pattern 3 and the transparent conductive pattern 5, moisture is penetrated between the metal thin film pattern 3 and the transparent conductive pattern 5 under the high temperature and high humidity circumstance. If moisture is penetrated between the metal thin film pattern 3 and the transparent conductive pattern 5, then an electrolytic etching reaction occurs between the metal thin film pattern 3 and the transparent conductive pattern 5. As a result, the metal thin film pattern 3 is corroded, and corrosion is progressed into the link pattern 4 and the driver IC 9 with the lapse of time.
Referring to FIG. 3, the conventional LCD device includes a shorting bar 15 commonly connected to a plurality of pads 11. Each pad 11 is connected to the data line or the gate line and includes a metal thin film pattern 12 patterned along with the source/drain electrode and a transparent conductive pattern 13 patterned along with the pixel electrode. The transparent conductive pattern 13 is connected, via a contact hole 14, to the metal thin film pattern 12.
The shorting bar 15 is connected to a ground voltage source GND during the fabrication process to be responsible for removing a static electricity applied to the liquid crystal display panel. The shorting bar 15 is formed from a metal at the edge portion of the lower substrate 1 corresponding to a non-display area. By the substrate scribing process and the grinding process, the shorting bar 15 is removed simultaneously when an unnecessary area at the edge of the lower substrate 1 is removed.
As shown in FIG. 4, a tape carrier package (TCP) 18 is attached to the pad 11 on the lower substrate 1 by a driver IC packaging technique adopting a tape automated bonding (TAB) system. The TCP 18
The TCP 18 is mounted with a data driver IC (or a gate driver IC) and is provided with input pads and output pads. The input pad of the TCP 18 is connected to a printed circuit board (PCB) (not shown). The output pad of the TCP 18 is connected to the pad 11 on the lower substrate 1. Herein, the input/output pads of the TCP 18 are connected to the PCB and the pads 11 on the lower substrate 1 by an anisotropic conductive film (ACF).
The ground face 16 exists in the side surface of the lower substrate 1 to which the TCP 18 is attached. The ground face 16 is formed by grinding the end of the pad area of the lower substrate 1 using a grinder (not shown) after the substrate scribing process. The end of the metal thin film pattern 12 is exposed onto the ground face 16. The exposed metal thin film pattern 12 is liable to be corroded under the high temperature and high humidity circumference. In other words, since one end at the cutting line side of a metal thin film layer 12a connecting the shorting bar 15 to the metal thin film pattern 12, corrosion is made through the metal thin film layer 12a. Such corrosion is progressed into the metal thin film pattern 12 of the pad 11. With the lapse of time, this corrosion is progressed until the gate line and the data line at the display area.
Accordingly, it is an object of the present invention to provide a liquid crystal display device that is capable of preventing metal wires from being corroded during its long-term use under the high temperature and high humidity circumference.
In order to achieve these and other objects of the invention, a liquid crystal display device according to one aspect of the present invention includes a pad positioned at a non-display area of a substrate to be connected to at least one of a gate line and a data line; a driving circuit for responding to an electrical signal from the pad to drive a liquid crystal pixel cell provided within said non-display area of the substrate; and a semiconductor pattern opposed to the driving circuit with having the pad therebetween to be connected between the pad and the driving circuit. The driving circuit is a driver integrated circuit connected to at least one of the gate line and the data line to drive any at least one of the gate line and the data line. The semiconductor pattern is formed from a poly silicon layer.
A liquid crystal display device according to another aspect of the present invention includes a plurality of pads connected to at least one of a gate line and a data line provided within a display area of a substrate; and a semiconductor pattern opposed to the gate line and the data line with having the pad therebetween and connected to the pad, said semiconductor pattern having one end exposed at the side surface of the substrate. The liquid crystal display device further includes a shorting bar connected to the semiconductor pattern upon fabrication process of the liquid crystal display device to apply a ground voltage to the gate line and the data line. The shorting bar is removed by a scribing process. The pads are connected to output pads of a tape carrier package mounted with a driver integrated circuit chip.
A method of fabricating a liquid crystal display device according to still another aspect of the present invention includes the steps of forming a pad at a non-display area of a substrate in such a manner to be connected to at least one of a gate line and a data line; forming a driving circuit for responding to an electrical signal from the pad to drive a liquid crystal pixel cell provided within said non-display area of the substrate on the substrate; and forming a semiconductor pattern opposed to the driving circuit with having the pad therebetween to be connected between the pad and the driving circuit on the substrate. The step of forming the semiconductor pattern includes forming a poly silicon layer on the substrate; and patterning the poly silicon layer.
A method of fabricating a liquid crystal display device according to still another aspect of the present invention includes the steps of forming a plurality of pads on a substrate in such a manner to be connected to at least one of a gate line and a data line provided within a display area of a substrate; and forming a semiconductor pattern opposed to the gate line and the data line with having the pad therebetween and connected to the pad and having one end exposed at the side surface of the substrate on the substrate. The above-mentioned method further includes the step of forming a shorting bar pattern connected to the semiconductor pattern to apply a ground voltage to the gate line and the data line at the edge of the substrate; and cutting the substrate along a cutting line set at the inside of the edge of the substrate provided with the shorting bar pattern to thereby remove the shorting bar pattern.